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Cruise control (also known as speed control, cruise command, autocruise, or tempomat) is a system that automatically controls the speed of an automobile. The system is a servomechanism that takes over the car's throttle to maintain a steady speed set by the driver. Another complaint we’ve heard is that the cruise control system operates more-or less fine, but tends to ‘hunt’, or constantly change throttle position from a little too much to a little too little, almost continuously while in operation. Found especially in higher-mileage vehicles, this is a clear symptom of a worn feedback potentiometer in the actuator. What happens is that the potentiometer resistance surface eventually wears out in just one small spot, and the only solution is a new actuator. That covers all 14 pins of the amplifier, and diagnosis is as simple as taking 14 readings (and 2 of them are grounds!).
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On the latest vehicles fitted with electronic throttle control, cruise control can be integrated into the vehicle's engine management system. Modern "adaptive" systems include the ability to automatically reduce speed when the distance to a car in front, or the speed limit, decreases. With the Tempomat (cruise control, (Distronic without radar)) plus automatic transmission, you can do your right foot a big favor.On longer journeys at constant speed it can hand over to the Tempomat. By means of a lever on the steering wheel you can select any desired speed above 30 km/h//19 mph and the Tempomat will maintain it. If the driver overrides the set speed by pressing the accelerator, for example when passing, upon releasing the pedal the vehicle will coast down and resume the set speed. It is important to avoid shifting into neutral in an automatic transmission vehicle, as this will cause the engine to rev up to the over-rev limiter setting.
References
An mentioned, vehicle speed is a series of pulses, with increasing frequency indicating increasing speed. In Mercedes-Benz vehicles with a mechanical speedometer cable, there is a sensor on the back of the speedometer that generates these pulses, while in electronic speedometer models the speedo re-forms the pulses received from the inductive sensor at the transmission output shaft. Since several other systems use the vehicle speed signal – CIS-E engine control, fuel pump relay, air conditioning and radio to name a few – there will be other systems affected if the vehicle speed signal is faulty. The cruise control takes its speed signal from a rotating driveshaft, speedometer cable, wheel speed sensor from the engine's RPM, or internal speed pulses produced electronically by the vehicle.
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Pins 9 and 13 are the throttle-position sensor power source and returned position voltage, respectively. The position sensor, which is a high-reliability potentiometer, is grounded at W1 along with the amplifier. Both the brake light switch and the cruise control system get power from Fuse 9, so a fuse failure ensures the system cannot operate.
If you are replacing a digital amplifier, you should swap the reference resistor over to the new amplifier. One frequently-heard complaint is a ticking or clicking sound coming from the actuator, along with the complaint that cruise control is inoperative. This is a symptom of a problem with the feedback potentiometer, where the amplifier believes (inaccurately) the throttle position is too high, causing the amplifier to run the actuator motor in an attempt to bring the throttle linkage to idle position. The clicking is the ratchet in the actuator clutch, since the actuator motor is also disengaged in this situation.
LIM – Electronic speed limiter
We have looked at each of the four major components and a few related systems and learned how they function and how they can be tested. We also became aware of a few Service Information bulletins with useful information for this convenience system. And finally we learned about a few of the more common complaints, learned their likely causes and how to correct them. The driver must manually bring the vehicle up to speed and use a button to set the cruise control to the current speed. A governor was used by James Watt and Matthew Boulton in 1788 to control steam engines, but the use of governors dates at least back to the 17th century.
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But as we mentioned, there are other components related to this system which may need to be checked as well. Using your ohmmeter, you can verify that all the switches are switching when they are supposed to, and by actuating them several times (including with more and less force) you can check for intermittent contacts. Because the switch’s connector contacts (down in the steering column) can also contribute to the problem, you might consider also measuring the switch values directly at the amplifier plug.
Components
Most systems do not allow the use of the cruise control below a certain speed - typically around 25 or 30 mph (40 or 48 km/h). The vehicle will maintain the desired speed by pulling the throttle cable with a solenoid, a vacuum-driven servomechanism, or by using the electronic systems built into the vehicle (fully electronic) if it uses a 'drive-by-wire' system. All cruise control systems must have the capability to be turned off explicitly and automatically when the driver depresses the brake pedal and often also the clutch. Cruise control systems frequently include a memory feature to resume the set speed after braking and a coast feature to reduce the set speed without braking.
Classic Mercedes-Benz Cruise Control – E-Tempomat System
Another inventor named Harold Exline, working independently of Riley, also invented a type of cruise control that he first installed on his car and friends' cars. Again, while these older models probably don’t make up the bulk of your customer base, we all know just how enthusiastic and passionate these classic-model owners can be. Your efforts at keeping their “baby” operating as designed will be appreciated by your customers, and likely profitable for you.
This symptom is often caused by a poor ground to the actuator at Pin 1 of the actuator connector, located in the engine compartment. Originally, the E-Tempomat control amplifier was a purely analog circuit, with a different part number for each vehicle. Since vehicles have different power-to-weight ratios, a different reaction by the amplifier is needed – for example, a 190D 2.2 needs to approach the throttle more aggressively when the speed drops, while the same reaction in a 560SL might be a little scary. Later versions, including the replacements available today, were digitally controlled, and a coding plug was attached to the amplifier to set the specific throttle response and other parameters.
Not sure if this helps, but for BMW Z3s they made a kit that allowed for you to just basically plug it in. I recommend going to dealership, get estimate, and then see if it has a part number you can cross reference for the kit to see if there are cheaper options online, or just buy the dealers kit. Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. 4MATIC is available on virtually every Mercedes-Benz vehicle so you should know the ins and outs, including service and maintenance recommendations. At the heart of the matter, the 4MATIC® system applies power to the front axles through a transfer case in the...
However, they will not apply the brakes in the event of overspeeding downhill, nor stop the car from going faster than the selected speed even with the engine just idling. As mentioned previously, the actuation switch has four inputs to the amplifier, on Pins 2, 3, 4 and 6. Pin 5 is the actuator clutch power output mentioned before, while Pins 7 and 10 control the actuator motor. The voltage on these two pins varies both in magnitude and polarity, since the DC motor used to actuate the throttle needs to be able to run in both directions and at variable speed.
On an engine, the governor uses centrifugal force to adjust the throttle position to adapt the engine's speed to different loads (e.g., when going up a hill). There was a time when superchargers and turbochargers were pretty much limited to race cars and certain high performance applications. Now, with the newer technology and the global drive for fuel efficiency and more power, turbochargers seem to be found on almost... Classic owners are passionate about their cars, and many can’t live without their cruise control.
The system ground (at W1) is connected to amplifier Pin 12 and (originally in production) Pin 14. At the time, there was a Dealer Technical Bulletin explaining the issue, but that document is no longer available. The system works by measuring vehicle speed and actuating the throttle linkage to increase or decrease engine output.
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